Top end miss

[hesermon]

Can anyone offer some suggestions? Under full throttle car takes off like a rocket, at about 3500 RPMs and 16 lb boost it begins to miss real bad, almost if it is being starved for fuel. If I back off and ease back into it, the miss is still there but much less drastic. Have changed so far, plugs, wires, coil pack, map, maf, cam sensor, tps. Taped fuel gauge to windshield, 55 lbs, no drop at high speed. Also put up on stands, no miss at high rpms without turbo spooling. Car has 42lb injectors, external waste gate, 3 inch ss exhaust, upgraded pump and reg. All this was done well before problem showed up.
Any suggetions would be greatly appreciated!

 

[Lee_Burough]

Can anyone offer some suggestions? Under full throttle car takes off like a rocket, at about 3500 RPMs and 16 lb boost it begins to miss real bad, almost if it is being starved for fuel. If I back off and ease back into it, the miss is still there but much less drastic. Have changed so far, plugs, wires, coil pack, map, maf, cam sensor, tps. Taped fuel gauge to windshield, 55 lbs, no drop at high speed. Also put up on stands, no miss at high rpms without turbo spooling. Car has 42lb injectors, external waste gate, 3 inch ss exhaust, upgraded pump and reg. All this was done well before problem showed up.
Any suggetions would be greatly appreciated!

I'd do some more checking on the fuel supply system.

You should have 45 PSI (fuel pressure) at idle with the vacuum line off (Assuming a TTA with a Bosch 237 FPR). If you have 16 PSI of boost at wide open throttle, you should see 45 + 16 on the FP gauge, or, 61 PSI of fuel pressure.

You could be running !!!lean!!!....You need to be using a scan tool at WOT. What are your scan tool readings at WOT?

If you don't see 45 PSI FP + boost value, you need a new fuel pump or FP regulator. Start by changing the fuel filter.

What concerns me most is that the 'miss' you report could actually be 'knock retard' (From, I suspect, running lean at WOT) ....That is a very bad thing for the health of your engine and could lead to a blown head gasket at the very least.

HTH

 

[philosobrad]

Just experienced this exact condition.....................................Ended up being two spotty injectors.

 

[Scott89TTA]

need some more info...are you stopping at 16 psi or are you going higher 18, 19, 20? My car did the same thing when I 1st got it after I installed the 3" maf pipe and K&N. I didn't have a scan tool and didn't realize I was getting 20+ psi boost...turned out to be bad knock. I installed a adjustable waste gate and turned down the boost and it went away almost...turned out I had bad plug wires and dead valve springs too. Once I changed out the springs and installed the new wires I could get 17-18psi with little to no knock with Eric's 93 street chip on 93 octane.

 

[hesermon]

thanks!

thanks everyone for the ideas. The fuel filter was one of the first things I tried. The car has always ran at least 18lbs of boost with no problems until recently. At highway speed I run 58-60 psi fuel pressure. When it begins to miss the gauge fluctuates between 55-58 lbs. Don't know if this is due to the miss in the engine or if this is causing the miss?? Set up is 42.5 lb injectors, TA-60 turbo, stainless 3" exhaust from turbo back (no cat), external waste gate, Bosch adjustable fuel press. reg., ATR fuel pump. 3200 stall non-lockup conv. Again, this is the set up that the car had when I bought it 5 years ago. My problem just started recently. The only changes I've made is to try to fix the problem.
Could a knock sensor cause these symptoms? I haven't changed it yet because it is such a B*#%h to get to. I keep thinking it is not fuel related because it runs fine without boost. (i.e. on stands without spool up it runs perfect). Also if I accelerate gradually there is no miss until about 16 lbs of boost.

 

[Razor]

I'd do some more checking on the fuel supply system.

If you don't see 45 PSI FP + boost value, you need a new fuel pump or FP regulator. Start by changing the fuel filter.

HTH

Anything under 60 PSI fuel at WOT===== You have a problem. Big one :redface:

1 PSI fuel for 1 PSI boost. 237 reg is 45 PSI. So 18 PSI boost=63 PSI fuel. You keep it at 55 PSI fuel=blown head gasket very very soon.

 

[Lee_Burough]

When Razor talks about tuning (or, just about anything else), I listen....You would do well to check your FP and FPR.

A little more detailed advice: Don't go WOT again until you have a scan tool! If you have less than about 760-770mv O2 at WOT when you get your 'miss', shut it down, you are running dangerously lean.

 

[hesermon]

Fuel pressure?

Thanks, Lee and Razor. I will replace the reg. first (since it is way easier than the pump). Is the Bosch 237 still the way to go or is there something better of late? As far as the pump, recommendations? Walbro? model? Which is the best Scan tool to get? Also have an 87 GN so I was hoping to get something portable. Used to have software for a laptop but was stolen with the car it was purchased for.
Thanks again, just so ya'll know, I'm not stupid enough to keep running WOT. It gets shut down as soon as the problem occurs. In fact it has taken some time to figure out the exact symptoms (at what fp, boost rpm's, etc.) because I shut it down immediately! Owned 5 years, about 4,000 miles put on it. Symptoms appeared less than 50 miles ago.

 

[Scott89TTA]

Get a Scanmaster ASAP...no modded GN/TTA should be without one...pretty much the 1st thing I got for mine. FULL THROTTLE SPEED - Item Description Page

As far as the AFPR I think most seem to run the Accufab these days.

Go here FULL THROTTLE SPEED - Items Page and look around

You also may want to go here Racetronix-TTA_Pump_Kit and get the Fuel Pump and Hot Wire kit too.

Listen to Razor and Lee...they know their s#!t ...that fuel pump is at least 5 years old...could very well be on it's way out :frown:

 

[Lee_Burough]

Thanks, Lee and Razor. I will replace the reg. first (since it is way easier than the pump). Is the Bosch 237 still the way to go or is there something better of late? As far as the pump, recommendations? Walbro? model? Which is the best Scan tool to get? Also have an 87 GN so I was hoping to get something portable. Used to have software for a laptop but was stolen with the car it was purchased for.
Thanks again, just so ya'll know, I'm not stupid enough to keep running WOT. It gets shut down as soon as the problem occurs. In fact it has taken some time to figure out the exact symptoms (at what fp, boost rpm's, etc.) because I shut it down immediately! Owned 5 years, about 4,000 miles put on it. Symptoms appeared less than 50 miles ago.

I'd call Full Throttle and get his recommendations for the pump and FPR, because that can vary with your performance goals. I liked the 237 because they used to be easy to buy for cheap and the new chips worked well for me. I used the Walbro pump. Mike L. will give you good advice for your combination and performance goals. There are others out there, but I've not dealt with them.